Ugandan security forces shot and killed at least three people and wounded several others in clashes with protesters after a fire gutted the tombs of four traditional kings.

The Kasubi tombs, a world heritage site in Kampala which includes the Buganda kingdom's 128-year-old mausoleum, was destroyed after catching fire last night. Baganda youths immediately blocked access to the hillside site, accusing the government of foul play.

There were further demonstrations today, when President Yoweri Museveni tried to visit the scene.

Lubega Segona, minister of information for the Buganda kingdom, said three people were killed and several wounded by members of the presidential guard.

"Those killed were among a crowd which was stopping the guards [from entering] where the tombs are located," said Segona. "The guards responded by opening fire."

The Buganda kings are known as kabakas. Their tombs have deep spiritual, political and religious significance for the Baganda ethnic group – the largest ethnic group in Uganda, with 6 million people – and the site is also a popular tourist attraction.

"The kingdom is in mourning," said John Walusimbi, prime minister of the Buganda kingdom. "There are no words to describe the loss occasioned by this most callous act."

With the cause of the blaze unclear, many protesters blamed the government.

The head of the Ugandan police, Kale Kayihura, described accusations of government involvement in the fire as "absolute falsehood", and said that a special committee had been established to investigate the cause.

Given their numbers, the Baganda represent an important political block. They supported Museveni when he took power in 1986. In turn, the president restored the country's four ancient kingdoms as cultural institutions in 1993, 27 years after former leader Milton Obote had abolished them. The kabakas, who are revered by many of their subjects, were granted ceremonial powers but told to keep out of politics.

Relations between the Baganda leadership and Museveni have soured in recent years following demands by the present kabaka, Ronald Muwenda Mutebi, for greater autonomy over the 9,000 square miles of kingdom land in central Uganda. This has been strongly rejected by the government. The tension boiled over last September after Museveni prevented Mutebi from visiting part of his kingdom. Protests in Kampala against the government's decision turned into riots, and left at least 15 people dead.